In a medium saucepan, combine the barley, stock, thyme and half of the garlic. Add a generous pinch of salt and bring to a boil. Cover and cook over moderately low heat until the barley is tender, 25 minutes. Discard the thyme. Drain the barley and transfer to a large bowl; cover and keep warm.
Meanwhile, in a large skillet, heat 1 tablespoon of the oil. Add the mushrooms, season with salt and pepper and cook over high heat, stirring, until lightly browned, 5 minutes. Add the shallots and cook, stirring, until softened, 3 minutes longer. Scrape the mushrooms into the barley and toss. Add the spinach, basil and mint, but do not stir.
Heat the remaining 1 tablespoon of oil in the skillet. Add the remaining garlic and cook over moderate heat until softened. Add the vinegar, lemon juice and brown sugar and bring to a boil. Cook until slightly thickened, 1 minute. Add the tomatoes and cook until heated through. Stir in the tofu and season with salt and pepper. Scrape the dressing over the salad and toss. Serve warm.